Optical switching using micro-electromechanical systems (MEMS) employs multiple micro mirrors that route signals carried on light beams from a fiber in a source bundle to a fiber in a destination bundle, each fiber being a port of the switch. The micro mirrors are typically electrostatically actuated and electronically controlled using various voltages, e.g., each micro mirror may require four independent voltages that are applied to various control electrodes so that the micro mirror may be operated through its full range of motion.
As the number of ports in a switch grows larger it becomes more difficult to couple the controlling voltages to the locations at which the electrodes are located on the substrate on which the micro mirrors are built. For example, for an array of 1200 input ports and 1200 output ports, which requires 1200 micro mirrors, 4800 electrodes must have voltages supplied to them. Using conventional techniques, which couple the voltage from the control circuits to the MEMS chip containing the micro mirrors using individual discrete wires, there are several failure modes that are exacerbated as the number of wires increases. Most importantly, since the failure probability of the electrical connections is relatively high, it is likely that if there is to be a failure in the switching system it will be caused by a failure of one of the connections. Multiplexing between the amplifiers generating the driving voltages and the electrodes is not possible, because if the voltage is not continually maintained the micro mirror will move, which will result in poor or lost optical connections.
One conventional approach that may be explored is to integrate the driving circuits onto the same substrate as the micro mirrors, or to directly couple the driving circuits to the substrate of the micro mirrors, e.g., using flip-chip or bump-bonding technology. Doing so would appear to provide several advantages of the device level, namely, it would a) reduce the number of connections, b) allow the use of high density wire routing on silicon using fine linewidth lithography, and c) reduce the number of wires that go to the micro mirror substrate by using multiplexing in the digital domain and employing demultiplexing on the substrate before the digital to analog conversion process is performed to generate each electrode's voltage.